Mention old-style exception support in CHANGES. (#60)

diff --git a/CHANGES b/CHANGES
index 2643f1e..bffefc8 100644
--- a/CHANGES
+++ b/CHANGES
@@ -5,6 +5,7 @@
   ProcessPoolExecutor
 - Set the default value of ``max_workers`` in ThreadPoolExecutor to ``None``, as in upstream code
   (computes the thread pool size based on the number of CPUs)
+- Added support for old-style exception objects
 
 
 3.0.5